Last week, Facebook said that 87 million of its users may have had their data inappropriately accessed by Cambridge Analytica, the British political data firm that worked on President Trump's 2016 election campaign.

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The data leak came after a Cambridge University researcher developed a personality-quiz app on Facebook's platform that downloaded people's data, which was then passed on to the political analytics firm.

FYI, it seems that after you view it once the notification doesn't show up again.

But here's a key point: You didn't need to take the Cambridge personality quiz for your data to get shared — all it took was for one of your Facebook friends to have done so. As such the 270,000 people who took the quiz gave the app access to tens of millions of their friends' data.